Asphaltic pavement.



E. M. GHADBOURNB.

ASPHALTIO PAVEMENT. APPLICATION FILED JAN. 7, 1914.

Patented July 1 1, 1914 ITED STAWENT OFFICE.

EDWARD M. CHADBOURNE, 0F TACOMA,

ASPHALTIC PAVEMENT.

Specification of Iietters Patent.

To all whom it may concern:

Be it known that I, EDWARD M. CHAD- BoURNE, a citizen of the United States, residing at Tacoma, in the county of Pierce and State of Washington, have invented certain new and useful Improvements in Asphaltic Pavements; and I do hereby declare the following to be a full, clear, and exact description of the same, reference being had to the accompanying drawings, forming part of this specification, and to the figures and letters of reference marked thereon.

This invention relates to the construction of pavements for roadways and more especially to that type wherein the surface is formed by a rock'or stoneaggregate combined with an asphaltic binder which is sub stantially non-fluid at ordinary temperatures, but is capable of being rendered limpid or liquid by the application of heat. The surface layer is usually supported by a suitable foundation such as cement or concrete and approved practice indicates the desirability of forming the surface of the foundation with pockets or irregularities, for example, such as referred to in my prior Patent No. 994,092.

The present invention is designed particularly as an improvement upon the process of my said prior patent, the objects being to simplify the process of laying the pavement to make a 'more uniform and homogeneous aggregate,"reduce the temperature necessarily employed, and to do away as far as possible with the necessity of handling any of the ingredients in a mlxed condition,

thus avoidingthe necessity of long hauls' and expensive mechanical mixing plants.

Asyinmysaid prior patented process, the present'process contemplates also .the use of an agglomerate which in its final condition is substantially free from voids and is thoroughly bonded together with no excess of twenty-five to forty per cent. of voids, for it is within these limits that effective capillary action will take place and the binder be held against draining away or accumulating in excess at, low spots.

Considerable difliculty is experienced in obtaining an asphaltic binder which is uniformly sufficiently limpid when heated, to accomplish the desired result of distribution through the heated aggregate entirely by capillary action. The difficulty is due to the fact that many asphaltic binders-are treated with dust, lime, etc., to give them body, and most of the natural asphalt binders, such as the Bermudez or Trinidad as'phalts naturally contains large amount of sediment, and this dust, 'lime or sediment, no matter whether. purposely placed in the asphalt, or found naturally therein, has a tendency to clog up the passages through which the asphalt should feed by capillary action, and with the result that a uniform distribution of the binder is interfered with. So, also, where capillary attraction alone is relied upon, the aggregate must be heated to a very high temperature in order to maintain the asphalt in a limpid condition for a sufficient length of time to effect the uniform distribution. Besides adding to the cost, the heating of the aggregate to a very high temperature always involves the risk of burning the asphalt or causing its quality to deteriorate, and the resultant mixture may contain A a larger percentage of binder than is necessary to secure the best results, for it is ob-= vious that where the binder is not uniformly 5 and evenly distributed, but is in excess at some points, the pavement will be unnecessarily soft in hot weather where such excessexists, and this may result in its destruction under heavy traffic conditions.

The present invention is desi' ed to overcome many, if not all, of these efects. which could not be foreseen but have been, to a Patented July 14, 1914'; Application filed January 7, 1914. Serial No. 810,866.

considerable extent, developed in the pracare distributed in layers they are mechanically mixed in sit/u b being turned over and over so that the capi lary action which takes place may proceed from various points of distribution, m to speak, inasmuch as the asphalt binder will be stirred up into "the aggregate. The mechanical mixing of the aggregate and binder in situ is preferably effected by drawing a rake-like implement backward and forward through the same, so as to efl'ect a thorough stirring Without causing the materials to segregate by reason of their difference in weight or size. Inasmuch as the binder is mechanically distributed through the aggregate it is obvious that the heat required is considerably less, as is also the time necessary to be allowed for the complete distribution of the binder by capillaryaction; L

In practice it is preferred to first spread the asphalt binder with a suitable templet, to the desired depth, said binder bein of the character referred to which is not impid or liquid at ordinar temperatures. The depth of the layer 0 asphalt binder varies 1n accordance with the' particular character of aggregate, and it is preferably determined empirically in a known way.

, Having spread the asphalt hinder, the heatthem thedepth of any layer orthe propor-v tion of asphalt and aggregate may be accuratelydetermined with great uniformity.

As soon as the hot aggregate has melted the asphalt binder the raking and stirrin' is commenced, and is continued until a t o ough uniform mixture will result bya com- Referring to the accompanying drawings,

paratively quick and uniform capillary action. After this stirring operation, the pavement is rolled in the well understood manner, and in accordance with common practice.

Figure 1 is a sectional view through a base with an asphalt binder s read evenly over the same; Fig. 2 shows t e binder covered p by an aggregate of hot sand and rock, the latter havin been spread with templets to the desired epth. Fig. 3 illustrates a rake with vaned prongs, arranged to mechanically mix and combine the asphalt and aggregate when drawn andpushed back and forth through the same; and Fig. 4 is a view showing the pavement completed and rolled.

In said drawings, the letter A indicates the base; C, the layer of normally non-fluid asphaltic binder spread on the base to a i uniform depth.

D is the hot layer of aggregate preferably having between twenty-five and forty per cent. of voids.

, proper F is the rake having the vaned prongs f for mixing the aggregate and binder after the binder has been rendered more or less limpid by the heat of the aggregate, and G indicates the finished pavement in which the aggregate and binder have been distributed to form a homogeneous mass, and the ing rendered limpid by the'application of heat, which consists in distributing the asphaltic binder and aggregate separately on a prepared foundation in layers of the proper depth to give the desired proportions when the layers are commingled, and in reducing the binder to a limpid condition by heating the same, then stirring the aggregate and binder in site. on the prepared foundation, and finally condensing, the commingled aggregate and binder by surface pressure.

.2. The method of constructing pavements composed of aggregate having its voids filled and the particles bonded together byasphaltic binder, which consists in spreading a layer of asphaltic binder on a suitable base, then spreading a loose layer of heated aggregate over the same the thickness of the two layers being such as to give the roportions for the'pavement when mixed, t en mixing the layers .of binder and heated aggregate by stirring the same on the base, then compacting the mixed aggre- "gate and binder by surface pressure.

. 3.- 'The method of constructing pavements,

havin a layer of mingled aggregate with its voids filled and the articles bonded together by asphaltic bin er non-fluid at ordinary temperatures but capable of being rendered limpid by heat, which consists in spreading separately a layer of asphaltic binder, and a layer of heated aggregate having between twenty-five and forty per cent. of voids therein, one over the other on a suitable roadway foundation, and in stirring. the two layers together, whereby capillary action is hastened by the mechanical distribution of the binder through the layer of aggregate and uniform distribu= tion of the binder is insured, and finally compacting the same by surface pressure. EDWARD M. CHADBOURNE. Witnesses: J. W. SroU'r,

A. SKOYEN. 

